In general, a radiation tube accelerates electrons emitted from an electron emitting source by a high voltage, and irradiates a target to thereby generate radiation, such as X-rays. The radiation generated at this time is emitted in all directions. PTL 1 discloses a transmission X-ray generating apparatus including an X-ray shielding member disposed on an electron incident side and an X-ray emitting side with respect to a target for shielding unnecessary X-rays.
It is required to apply a high voltage between the electron emitting source and the target to irradiate the target with a high energy electron beam, to generate radiation suitable for radiation imaging. However, in general, the radiation generation efficiency is quite low, and about 99% of the power consumed becomes heat.
The generated heat elevates the temperature of the target, which necessitates some means for preventing the target from being thermally damaged. PTL 2 discloses an X-ray generating tube that includes a cooling mechanism around an X-ray transmission window to thereby improve the heat radiation efficiency for the target portion.